M4(1) SysV M4(1)
NAME
m4 - macro processor
SYNOPSIS
m4 [ options ] [ files ]
DESCRIPTION
m4 is a macro processor intended as a front end for Ratfor, C, and other
languages. Each of the argument files is processed in order; if there
are no files, or if a file name is -, the standard input is read. The
processed text is written on the standard output.
OPTIONS
-e Operates interactively. Interrupts are ignored and the output
is unbuffered.
-s Enables line sync output for the C preprocessor (#line ...)
-Bint Changes the size of the push-back and argument collection
buffers from the default of 4,096.
-Hint Changes the size of the symbol table hash array from the
default of 199. The size should be prime.
-Sint Changes the size of the call stack from the default of 100
slots. Macros take three slots, and non-macro arguments take
one.
-Tint Changes the size of the token buffer from the default of 512
bytes.
To be effective, these must appear before any file names and before -D or
-U:
-Dname[=val]
Defines name to val or to null in val's absence.
-Uname
Undefines name.
Macro calls have the form:
name(arg1,arg2, ..., argn)
The left parenthesis ( must immediately follow the name of the macro. If
the name of a defined macro is not followed by a (, it is deemed to be a
call of that macro with no arguments. Potential macro names consist of
alphabetic letters, digits, and underscore _, where the first character
is not a digit.
Leading unquoted blanks, tabs, and new-lines are ignored while collecting
arguments. Left and right single quotes are used to quote strings. The
value of a quoted string is the string stripped of the quotes.
When a macro name is recognized, its arguments are collected by searching
for a matching right parenthesis. If fewer arguments are supplied than
are in the macro definition, the trailing arguments are taken to be null.
Macro evaluation proceeds normally during the collection of the
arguments, and any commas or right parentheses which happen to turn up
within the value of a nested call are as effective as those in the
original input text. After argument collection, the value of the macro
is pushed back onto the input stream and rescanned.
BUILT-IN MACROS
m4 makes available the following built-in macros. They may be redefined,
but once this is done the original meaning is lost. Their values are
null unless otherwise stated.
define Installs the second argument as the value of the macro whose
name is the first argument. Each occurrence of $n in the
replacement text, where n is a digit, is replaced by the n-th
argument. Argument 0 is the name of the macro; missing
arguments are replaced by the null string; $# is replaced by
the number of arguments; $* is replaced by a list of all the
arguments separated by commas; $@ is like $*, but each argument
is quoted (with the current quotes).
undefine Removes the definition of the macro named in its argument.
defn Returns the quoted definition of its argument(s). It is useful
for renaming macros, especially built-ins.
pushdef Like define, but saves any previous definition.
popdef Removes current definition of its argument(s), exposing the
previous one, if any.
ifdef If the first argument is defined, the value is the second
argument, otherwise the third. If there is no third argument,
the value is null. The word unix is predefined on UNIX system
versions of m4.
shift Returns all but its first argument. The other arguments are
quoted and pushed back with commas in between. The quoting
nullifies the effect of the extra scan that will subsequently
be performed.
changequote
Changes quote symbols to the first and second arguments. The
symbols may be up to five characters long. Changequote without
arguments restores the original values (i.e., `').
changecom Changes left and right comment markers from the default # and
new-line. With no arguments, the comment mechanism is
effectively disabled. With one argument, the left marker
becomes the argument and the right marker becomes new-line.
With two arguments, both markers are affected. Comment markers
may be up to five characters long.
divert m4 maintains 10 output streams, numbered 0-9. The final output
is the concatenation of the streams in numerical order;
initially stream 0 is the current stream. The divert macro
changes the current output stream to its (digit-string)
argument. Output diverted to a stream other than 0 through 9
is discarded.
undivert Causes immediate output of text from diversions named as
arguments, or all diversions if no argument. Text may be
undiverted into another diversion. Undiverting discards the
diverted text.
divnum Returns the value of the current output stream.
dnl Reads and discards characters up to and including the next
new-line.
ifelse Contains three or more arguments. If the first argument is the
same string as the second, then the value is the third
argument. If not, and if there are more than four arguments,
the process is repeated with arguments 4, 5, 6 and 7.
Otherwise, the value is either the fourth string, or, if it is
not present, null.
incr Returns the value of its argument incremented by 1. The value
of the argument is calculated by interpreting an initial
digit-string as a decimal number.
decr Returns the value of its argument decremented by 1.
eval Evaluates its argument as an arithmetic expression, using 32-
bit arithmetic. Operators include +, -, *, /, %, ^
(exponentiation), bitwise &, |, ^, and ~; relationals;
parentheses. Octal and hex numbers may be specified as in C.
The second argument specifies the radix for the result; the
default is 10. The third argument may be used to specify the
minimum number of digits in the result.
len Returns the number of characters in its argument.
index Returns the position in its first argument where the second
argument begins (zero origin), or -1 if the second argument
does not occur.
substr Returns a substring of its first argument. The second argument
is a zero origin number selecting the first character; the
third argument indicates the length of the substring. A
missing third argument is taken to be large enough to extend to
the end of the first string.
translit Transliterates the characters in its first argument from the
set given by the second argument to the set given by the third.
No abbreviations are permitted.
include Returns the contents of the file named in the argument.
sinclude Is identical to include, except that it says nothing if the
file is inaccessible.
syscmd Executes the UNIX system command given in the first argument.
No value is returned.
sysval Is the return code from the last call to syscmd.
maketemp Fills in a string of XXXXX in its argument with the current
process ID.
m4exit causes immediate exit from m4. Argument 1, if given, is the
exit code; the default is 0.
m4wrap Argument 1 is pushed back at final EOF; example:
m4wrap(`cleanup()')
errprint prints its argument on the diagnostic output file.
dumpdef Prints current names and definitions, for the named items, or
for all if no arguments are given.
traceon With no arguments, turns on tracing for all macros (including
built-ins). Otherwise, turns on tracing for named macros.
traceoff Turns off trace globally and for any macros specified. Macros
specifically traced by traceon can be untraced only by specific
calls to traceoff.
SEE ALSO
cc(1), cpp(1).